1. Field of Invention
The invention relates to a carbon base member that may be used in components such as the commutator segments of commutators in electric motors and a process for producing the carbon base member.
2. Description of Related Art
In general, in an in-tank type fuel pump mounted on vehicles, the inside space of a housing constituting the fuel pump serves as a passage through which a fuel such as gasoline flows because the fuel pump itself is sunk (immersed) in the fuel. In such a system, it is necessary that the materials used to fabricate the fuel pump are formed using materials that are not damaged by the corrosive action of the fuel.
Recently, blended fuels containing a mixture of gasoline and alcohol or the like have become more widespread as a result of heightened interest in protecting the environment. However, it is known that the copper components fuel pumps for gasoline fuel can become corroded when used with these blended fuels. In particular, it is generally the commutator of a conventional electric motor, which is incorporated into a gasoline fuel pump, that is corroded by the alcohol.
U.S. Pat. No. 5,175,463 describes the structure of a typical commutator segment. Generally, a commutator segment is made of carbon at the portion with which a brush slidably contacts the commutator segment (carbon material) to minimize the corrosion caused by alcohol. The commutator segment is formed with a metal layer on the surface (one surface of the carbon material) opposite to the portion that slidably contacts the brush. A conductive terminal member (riser bar) made of copper is integrated (electrical connection) with the metal layer. However, the carbon material is known to have poor surface wettability and is therefore difficult to bind with almost all metals. In order to bind the conductive terminal member with the surface of the carbon material, it is necessary to form a metal layer between them. For this, according to the aforementioned patent, the surface of the carbon material is plated using nickel or the like and the conductive terminal member is bound to the plated surface by means of, for example, soldering. In this case, the metal layer formed by plating can be easily peeled off. Thus, even if integrated bonding between the metal layer and the conductive terminal member could be accomplished, the possibility that the plated metal layer, together with the conductive terminal member, may peel from the surface of the carbon material. The strength of adhesion between the metal layer and the carbon material may be insufficient for a suitable commutator and results in inferior durability.
In addition, JP-A-8-308183 shows a structure with a carbon base member, to which a conductive terminal member has been bound in advance, that is formed by unitedly sintering a carbon powder, a metal powder arranged layer-like to the carbon powder and the conductive terminal member arranged on the metal powder side.
However, because this is a configuration in which a carbon powder, a metal powder and a conductive terminal member are sintered integrally, the sintering process is complicated and poses many difficulties. For example, the sintering temperature must be carefully selected to be a temperature that is of the order at which the conductive terminal member made of copper is not deformed and lower than the melting point of the metal powder. This severely limits the range of temperatures that may be used to sinter the carbon material. Furthermore, when sintering these different materials together, the differences in the sintering shrinkage percentage between the metal powder and the carbon powder can lead to the formation of a clearance between them very easily. There is, therefore, a fear that the sintered metal and carbon layers may peel from each other. In order to prevent this, it is necessary to select a carbon material that has a sintering shrinkage percentage that is similar to that of the metal powder. However, this solution to prevent peeling then limits types of carbon material that may be selected, which excludes the use of certain carbon materials having the desired characteristics for a particular application. The problem to be solved by the present invention consists in this point.
In view of the above problems, the invention has been made for the purpose of solving these problems. In one embodiment, the invention provides a carbon base member comprising an iron layer formed on the surface thereof and bondable with a metal material. The carbon base member is formed by sticking an iron powder to a carbon material formed in advance by sintering, and by sintering the resulting product at a temperature higher than the diffusion temperature of carbon and lower than the melting point of iron. According to the invention, an inclined function material can be made in which the metal layer is securely formed on the surface of the carbon material unitedly.
Further, the invention provides a process for producing a carbon base member comprising an iron layer formed on the surface thereof and bondable with a metal material. The process comprises sticking an iron powder to a carbon material formed in advance by sintering, and thereafter sintering the resulting product at a temperature higher than the diffusion temperature of carbon and lower than the melting point of iron.
According to this process, the sintering temperature of the carbon material can be designed arbitrarily, so that the characteristics of the carbon base member can be selected in a free manner.
In the invention, an appropriate sintering temperature may be designed to be 1000 to 1300xc2x0 C.
Further, in the invention, the iron powder may be fine particles having an average particle diameter of 10 xcexcm or less.
Also, in the invention, the carbon base member may be used as a commutator segment constituting an electric motor.
Moreover, in the invention, the surface of the carbon base member may be provided with a conductive terminal member bonded therewith.